The integration of hundreds of millions of circuit elements, such as transistors, on a single integrated circuit necessitates further dramatic scaling down or micro-miniaturization of the physical dimensions of circuit elements, including interconnection structures. Micro-miniaturization has engendered a dramatic increase in transistor engineering complexity, such as the inclusion of graded well-doping, epitaxial wafers, halo implants, tip implants, lightly doped drain structures, multiple implants for source/drain regions, silicidation of gates and source/drains, and multiple sidewall spacers, for example.
The drive for high performance requires high speed operation of microelectronic components requiring high drive currents in addition to low leakage, i.e., low off-state current, to reduce power consumption. Typically, the structural and doping parameters tending to provide a desired increase in drive current adversely impact leakage current.
Metal gate electrodes have evolved for improving the drive current by reducing polysilicon depletion, and reducing processing temperature subsequent to metal gate formation. In order to implement replacement metal gate process flow, a dummy gate, such as polysilicon, is removed by dry/wet etching, followed by metal deposition.
The relentless drive toward greater miniaturization requires a reduction in the feature size of transistors, including gate oxide layers for metal gate transistors. Such gate oxide layers must be reduced to achieve a very thin effective oxide thickness (EOT). This objective has been illusive in attempting to form gate oxides at thicknesses of about 15 Å because of the leakage current.
Accordingly, there exists a need for metal gate transistors having a gate oxide with a reduced EOT with reduced leakage current. There also exists a need for methodology enabling the fabrication of semiconductor devices comprising metal gate transistors having a gate oxide with a reduced EOT without sacrificing device speed.